well. u have a method computePayment(double la, double yi, int py, double mp)in the Interest Class for which we have to send four parameters means four values as an arguments. But when you are calling the same method in the first switch statement u use the statement loan1.computePayment(). there we are not sending any parameters.

You can fix in two ways
1. Remove the parameters in the method definition inside the Interest class for all the methods.
2. Pass four parameters when you call the particular method in each of the switch class.